$\mathrm{R}-\mathrm{X}\stackrel{\mathrm{Z}}{\to }\mathrm{R}-\mathrm{OH}$. Z cannot be 

$\begin{array}{c}{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{Cl}\\ {\mathrm{C}}_2{\mathrm{H}}_5\mathrm{Cl}\end{array}+{\mathrm{Ag}}_{2}O\to {\mathrm{C}}_2{\mathrm{H}}_5-\mathrm{O}-{\mathrm{C}}_2{\mathrm{H}}_5+2\mathrm{AgCl}$

$\stackrel{{\mathrm{sp}}^3}{{\mathrm{CH}}_3}-\stackrel{{\mathrm{sp}}^3}{{\mathrm{CH}}_3}-\stackrel{{\mathrm{sp}}^3}{\underset{••}{\overset{••}{\mathrm{O}}}}-\stackrel{{\mathrm{sp}}^3}{{\mathrm{CH}}_2}-\stackrel{{\mathrm{sp}}^3}{{\mathrm{CH}}_3}$

Total number of ${\mathrm{sp}}^3$ hybrid orbitals = 4 + 4 + 4 + 4 + 4 = 20

Total number of ${\mathrm{sp}}^3$ hybrid involved in bonding = 20 - 2 = 18

Two of the ${\mathrm{sp}}^3$ hybrid orbitals of oxygen have lone pairs 

Dry ${\mathrm{Ag}}_2\mathrm{O}$ converts R - X to R - O - R